When an operator works in contact with a live-line, safety measures must be taken against strokes. As a rule, working should be carried out under equipotential conditions. In other words, the operator and the power line are placed in mutual electric contact to be at the same potential, whereas the operator is adequately insulated from the ground or from other objects at potentials other than that of the line. This will prevent direct passage of current through the operator's body. For example, the operator may work on a live line from an aerial insulating platform or be kept proximate to the live line by a helicopter.
In order to achieve and maintain equipotential conditions, a safety cable must be kept connected at one end to a live-live element as a bare conductive cable, and at the other end to objects in contact with the operator, such as gloves or other conductive garments, as well as with the operator-supporting structure, such as the insulating platform or the helicopter.
In order to ensure connection of the safety cable to the live element of the power line, coupling tools are commonly used, such as clamps or snap hooks, similar to those used on scaffolds for safety against the risk of fall. Such coupling tools have two jaws, which are held together in a closed configuration by a spring. In the closed configuration, the jaws surround the live-line element and hold it in a space therebetween.
In order to insert the live element into the two jaws and remove it therefrom, at least one jaw is pivoted relative to the other, against the action of a spring, to an open configuration in which a passage is created for insertion and/or removal of the live element into/from the space between the jaws.